Astigmometer



Jan. 7, 1936. T, ABENNETT 2,026,607

ASTIGMOMETER Filed oct. so, 1955 v2 sheets-sheet 1 F G.- l.

INVENTOR:

THEODORE A. BENNETTl *BY Cay( ATT'YS.

Patented Jan. 7, 1936 UNITED STATES PATENT OFFICE 3 Claims.

The present invention relates to an astigmometer used by eye examinersfor determining whether a patient has astigmatism, how much theastigmatism is, and the amount of correction necessary to make thepatients vision as nearly normal as possible. It is also used for thepurpose of determining the cylindrical power of the lens required tocorrect the astigmatism.

One object of this invention is to provide a means and method forquickly and accurately locating the ametropic correction necessary foran eye.

Another object of this invention is to provide means for locating theprimary and secondary principal meridians of the patients eye, which isnecessary in order to construct a lens to correct the astigmatism.

Another object of this invention is to provide a simple method andmechanism for determining the amount of correction necessary inconjunction with standard test lenses.

Another object of this invention is to provide an instrument for quicklychecking a patients old lenses while the same are being worn, for thedetermination of possible errors in the positions of the axes of thelenses or in the "cylinder correction.

Another object of this invention is to provide a simple mechanism whichcan be operated by the patient himself for determining the primary andsecondary principal meridians of the eye.

Another object of this invention is to provide an instrument havingsuitable charts which may be viewed either directly by the patient or ina mirror and including associated instrumentalities providing suitableangular indicating means for compensating for the reversed image of thechart viewed in the mirror by the patient, so that whichever way thechart is used, the correct angles will be indicated. This aspect of theinvention includes an arrangement whereby the axes are indicateddirectly in degrees, regardless of whether the instrument is used with-a mirror or is viewed directly by the patient.

Another object of this invention is to provide a new and improved methodfor determining the primary and secondary principal meridians of theeye.

Another object oi this invention is to provide an improved method andapparatus for determining the primary and secondary principal meridiansin a quicker and more accurate manner than is possible with otherinstruments in use at the present time.

Another object of this invention is to provide (C1. Sii-20) preferablywith suitable black parallel lines, l0

which are rather narrow as compared with prior practice, and which arespaced apart considerably in proportion to their Width, with the spacestherebetween being white or of a contrasting shade or color, so that thepreponderance of the l5 chart used will appear to be white or ofthecontrasting shade or color used, thereby enabling the determination ofthe meridians quickly and accurately, due to the fact that the positionof the lines when in alignment with the primary principal meridian willappear real black, and any slight deviation therefrom produces a blurreadily and immediately observable by the patient.

Another object of this invention is to produce a simple, efficientmechanism for the purposes set forth and provide in connection therewithcertain novel elements which make the device simple, durable, andeflicient.

Other objects of this invention will appear hereinafter as thedescription of this invention proceeds, the novel features, arrangementsand combinations being clearly set forth in the appended claims.

In the drawings:

Fig. 1 is a front elevational View of a device embodying my invention,showing the position of the parts when the 'device is to be vieweddirectly y bythe patient; y

Fig. 2 is a fragmentary front elevational view of the left half of theinstrument shown in Fig. 1 with the parts in another position ofadjustment.

Fig. 3 is a. cross-sectional View taken on the line 3-3 of Fig. 5;

Fig. 4 is a rear elevational view of the instrument with parts brokenaway for the sake of clearness; Y t v Fig. 5 is a verticalcross-sectional view taken on the line 5-5 of Fig. 1;

Fig. 6 is ,a cross-sectional view taken substantially along the line 6-6of Fig. 5.

Fig. '7 is a schematic view illustrating the manner in which thisinstrument is used With a mirror.

A discussion of what constitutes astigmatism is not necessary here, asit is well knownv in the art; sufcient to say, that in correcting forastigmatism, one must first find the primary and secondary principalmeridians of the eye. With known methods, this primary principalmeridian is very diflicult to determine exactly or within very narrowlimits, because some tests are so complicated that they do not enablethe patient (who is the judge) to determine at what exact angle certainlines appear blackest to him, thus establishing the position of theprimary principal meridians, and unless the patient can determine justwhat lines at various angles appear blackest to him or at what anglecertain lines appear blackest to him, it is impossible for theOptometrist to determine the primary principal meridian with any degreeof accuracy. Some of the difficulties which the patient experiences intrying to determine at what position certain lines appear darkest to himarise from the fact that his attention is directed to more than onevisual obj ject at the same time, and he cannot fully concentrate onwhat he is doing as well as when his mind is concentrated only on onething at a time. Other known methods are not sufficiently accurate togive good results, and the impressions which the charts are supposed toimpart to the patients eye are not sufficiently definite to enable thepatient to describe them accurately, with the result that frequently thepatient becomes confused and describes what he sees as being differentfrom the impression that he should receive. For instance, some of theimpressions which the patients eye is supposed to receive are describedby the Optometrist as being checker-board, honey-combed, stair effect,and the like. The patient, however, may be trying to describe acondition between a true checker-board effect and a honey-comb effect.This oftenresults in the location of the improper primary meridian ofthe eye. Thus, he is not able to fit the patient with the proper glassesfor his astigmatism. However, by using as I do, the lines whichv arevery narrow with wide intervening light spaces, the patient is betterable to determine at just what angle the lines appear to be blackest tothe eye.

Referring now to a detailed description of the invention, in thedrawings, the reference character IU indicates the base of theinstrument which has identical upstanding pedestals II formed integraltherewith, and, as clearly indicated in Fig. 6, each of these pedestalsis provided with a bushing I2 rotatable within a bearing I3, at the topthereof. I will describe only one of these pedestals and the mechanismsupported thereby, as the details of both are identical, except forslight differences which will be pointed out hereinafter. The bushing I2is provided `with a peripheral groove I 4, and a set screw I5, threadedthrough the bearing, has the end thereof extending into this groove toprevent longitudinal movement of the bushing. Lock nut I5 holds thescrew in adjusted position. However, the bushing can rotate freely onits axis through at least 180 degrees. The bushings are connected bymeans of a flexible band I6, the ends of which are connected by a turnbuckle I'I,Hwhich is used to tighten the band. The band is preferablymade of flexible metal, but can be made of fabric or any other desiredmaterial. Also, instead of using a flat, endless band of metal such asshown,'I can use a flexible chain, gearing or the like. The

' purpose of the connection between the two bushings Ii?. is merely toimpart to these bushings equal amounts of rotative movement so that whenone of the bushings is rotated by means presently to be described, theother bushing will also rotate.

The bushing I2 is provided With a stem IB, integral with or secured to aweb portion I9, the axis of the stem I8 being concentric with the axisof the bushing I2. The stem carries a hand wheel I 9', which can bemanipulated to rotate the stem and bushing, and is secured thereto inany desired manner.

Each of the bushings I2 supports a reflector 20 which hascylindrical'portions 2I thereof forced into the bore of the bushing sothat the reflectors will rotate with the bushing. The flexible band I6is secured to each of the bushings I2 by means of screws 22, which, froman inspection of Fig. 3 are threaded into the bushings in such a mannerthat at least 180 degrees of rotation may be imparted to the bushings.While the press fit of the cylindrical portions 2I of the reflectors inthe bushings is sufficient to ordinarily hold the cylindrical portionand bushing against relative rotation, nevertheless, it is preferredthat the screws 22 extend through the bushings, and also through thereflectors, as is clearly illustrated in Fig. 5, to positively preventsuch relative movement.

Within each of the cylindrical portions 2I, there is provided a lampsocket 23, suitably secured within the cylindrical portion as by meansof the hollow threaded portion 24 on the socket, and the nut 25. Anordinary incandescent bulb is screwed into the socket 23, and the raysof light are reflected by the reector through a translucent chart 26,secured over the opening in the front of the reflector. The constructionof this chart will be described later. Each reiiector has securedthereto an annular flat disc portion 21, on which there are suitablegraduations also to be described later. The annular disc 2'I has aflange 28 embracing the peripheral bead 29 on the reflector and setscrews 30 arranged peripherally about the flange 28, engage the rearside of the bead 29 and hold the disc portion 21 on the reflector aswell as exert a camming effect which draws the disc portion 2'I inwardlytoward the reflector to clamp the chart 26 between the portion 3I of thedisc 21 and the bead 29, on the reflector.

The chart 26 is made of 2 flat glass discs 32 and 33, the former beingpreferably clear glass with opaque lines 34 painted, etched and thenpaintedA or otherwise placed thereon, on the side opposed to disc 33,and the disc 33 is opalescent to diffuse the light from the bulb I5" asit passes through the chart. The lines 34 are preferably about 5%" inwidth and spaced about 1/2" to 3A" apart. I have found that such widthsand spacing giveY excellent results. Of course, the positions of theblack lines between the discs is only the preferred position, for it isobvious that the lines could be elsewhere than `as indicated, but in thepreferred positions the lines are protected and will not lose theirblackness as they might if exposed and subject to contact by cleaningcloths or the like which may be used to clean the instrument. The edgesof the discs 32 and 33 are held together by a peripherally extendingband 33', preferably of yielding or adhesive material to prevent theirseparation and to exclude dust therefrom. VThe clamping effect of screws30 also assists in holding these plates together.

With this arrangement, whenever the bushings are rotated by actuatingone of the hand wheels I9 the charts, reflectors, and discs 2'I rotatein unison and since the latter are set in fixed relation to the lines onthe charts, the same are marked or graduated to indicate the angles ofthe lines v34 with respect to agiven zero position (in this case ahorizontal line) from which the optometrist works. These graduations aredivided into two sets on each disc. The shaded areas of discs421 areherein designated as scales A and A. The unshaded areas are designated Band B with scales A and B arranged about chart C and scales A and Barranged about chart C. Each scale indicates angles up to 180%.

Pointers D and D are adapted to cooperate with scales 'A and A when saidscales are being used in testing the patient by having him View thecharts directly, whereas pointers D and D' cooperate with scales B and Bwhen said scales are being used in testing the patient by havingr himview the charts in a mirror. Since the bushings I2 have only 180 ofrotation only one set of scales A-A or B-B' can be used at one time andwhen the other set of scales are to be used the screws 30 are loosenedand the discs 2'I rotated 180 relative to the reflectors whereafter thescrews are again tightened and the 'other sets of scales are in positionto be used with pointers D and D'. Gears could be used suchVthat-bushings I2 would have 360 of rotation, but while this wouldeliminate shifting the charts and discs through'180 in the manner setforth, the operator might use the 4wrong set of scales when testing thepatient and gross inaccuracies would result, whereas with the describedarrangement, this will not happen, and generally one setting is enough,as the Optometrist either uses one or the other methods of testingexclusively, or at least only changes in rare cases. Thus when once setthe Optometrist is prevented from incorrectly reading the Vtrue primarymeridian of the eye after the chart is setduring the'tests.

The scales A, A', B, and B are so graduated that they read directlytheangles of the primary and secondary meridians of the eye measured in aclockwise .direction from the horizontal, 'when the lines 34 on chart Care at the angle where the same appear darkest to the'patient.

The pointers D and D are secured by screws 35 to the ends of rods 36which in turn extend through openings 31 in the base and are heldtherein by screws 38.

An electric cord 39 having a plug 40 thereon to be connected to a socketin a light circuit, extends into the base I and has branches 4I whichextend upwardly through pedestals II, then out of same throughinsulating bushings 42, next into bushings I2 through insulatingbushings 43 Y in caps 44, which are secured over the ends of thebearings I3 by screws 45, and iinally into lamp sockets 23 to suitableterminals therein. In Fig. 6 it will be noted that due to the largespace "I6 provided by having the web I9 extend considerably less than180, the cord extension 4I is not engaged by the webs and thus the lifeof the cords is lengthened, as the bushings I2 have only 180 of rotationor perhaps rotation just slightly in excess thereof.

Independent switches E and E' are used to send the current to the bulbsI5 behind the respective charts C and C so that either or both can beilluminated as desired.

I will now describe the operation of my device as used in practice.FirstV I will describe the direct method, which is the one Where thepatient sits in front of the instrument generally at the prescribeddistance of 20 feet.

Each eye is examined separately. The charts are set to use scales A andA. The patient sits erect with hiseye focused on chart C, which is theonly one which is illuminated at rst. The strongest plus spherical lensor the weakest minus spherical lens that he can have and stilldistinguish the lines on the chart in one position of the chart only, isthen placed between the eye of the patient and the chart. This provesthe presence of astigmatism, as otherwise the lines would appear equallyblack in al1 positions of the chart.

To determine the exact axis of astigmatism, the Optometrist rotates thechart C slowly to each side of the position where the lines appearblackest and the patient is then instructed to tell when the lines beginto blur. The angular positions where blur occurs are noted on scale A atpointer D and then the scale is moved to the position equidistant fromthe two positions where the lines begin to blur. This is the primaryprincipal meridian and the axis of the plus cylinder lens. The otherchart C is then illuminated and if the system has been properly appliedthe lines on the second chart C will be blurred, because the secondchart automatically assumes a position establishing the secondaryprincipal meridian and the axis of the minus cylinder lens. TheOptometrist next proceeds to equalize the lines on both charts inclearness and blackness by suitable cylinder lenses, always using aminus cylinder lens with axis set at the secondary principal meridian ofthe eye. The amount of cylinder lens ,power necessary to equalize thelines on both the charts in clearness and blackness is the amount of theastigmatism- The lens or combination oi lenses now f' found before theeye should be the approximate ametropic correction. The power of thespherical lens should only be varied if necessary to irnprove the acuityof theeye. This is repeated for the other eye and glasses ttedaccordingly.

Tovuse this device with a mirror, or by the indirect method, the patientsits behind the instrument looking over the same into a mirror 4l (seeFig. '7) in which are reiiected the images of the charts, the positionof the eye being indicated at 48 and the instrument being indicatedgenerally at 49. Y In this position the patient can turn the hand wheelsI9 himself and thus stop rotation of the charts more readily at thepositions where the lines are blackest or begin to be blurred. Theoptometrist notes the angles on the charts B and B which are used withthis method and locates the meridians as before. The scales B and B arearranged to compensate for the changed angles of the Vlines relected sothat the angles read on scales are angles of the lines as they appear inthe mirror.

In Fig. 1 the scales A and A are being used for direct use of theinstrument, that is, the charts are to be viewed directly by thepatient, while in Fig. 2 the scales B and B are being used, disc 21having been rotated 180 relative to the reflector from its position inFig. 1. If the lines 34 as shown in Fig. 2 are reiiected in a mirror, itis obvious that their appearance to the patient will be the saine as thelines on this chart in Fig. l. Therefore, the pointer D should indicatethe same angle on scale B' in Fig. 2 that-it does on scale A in Fig. 1,which it does, as will be seen from an inspection of these figures.

This instrument can be used for other purposes, such as for locating theaxis of a lens, and for doing this the indirect method lis used. Theperson making the test must have his eyes free from astigmatism. or haveany astigmatism therein corrected for, before this test' can be properlymade. The spherical power of the lens is neutralized to leave a cylinderof plus denomination. The lens is held in the same position which itwould occupy when in front of the patients eye. The chart is thenrotated to the position where the lines are clearest, and this will bethe axis of from axis oi the plus cylinder under observation. The axisof the cylinder being checked will be indicated on scale of chart notlighted. The instrument can also be used in this manner to check theglasses which the patient is wearing, to see if they are what he shouldbe wearing.

This instrument is very efficient, since the charts show a preponderanceof white which merges more quickly with the black to produce noticeableblurs, than with other instruments; it is simple, yet speedy, as onlyone chart is used to check the eye for one meridian and the othermeridian is determined automatically; there are no lines except in onemeridian; and the patient can operate the instrument himself.

If desired, two pointers can be used for each chart one with scale A orA and the other for B or B'. 'Ihese would be situated 180 from eachother and suitably graduated to indicate the proper angles of the lineson the charts. This arrangement is not as satisfactory as that shown,for, while it does away with moving the charts angularly when one wishesto change from one method of testing to the other, the Optometrist isapt to read the wrong pointer and as a result get the wrong angles ofthe principal meridians, or the two scales and cooperating meanstherefor could be otherwise arranged conveniently, but that arrangementshown is preferred.

Those skilled in the art to which this invention pertains may make otherchanges in the construction o1- arrangement of parts without departingfrom the spirit of this invention or the scope of the appended claims,and therefore I do not wish to be limited except as set forth in theappended claims.

Having thus iully described one embodiment of my invention, whatI claimand desire to secure by Letters Patent or the United States is:

1. An astigmometer comprising a pedestal having a bearing thereon, abushing journalled in said bearing for rotative movement, a reflectorcarried by said bushing rotatable therewith, and having an open side,illuminating means within said reector, a transparent chart arrangedover said open side, and indicating means for indicating the angularposition of said chart.

2. An astigmometer comprising a pedestal having a bearing thereon, abushing journalled in said bearing for rotative movement, a reilectorcarried by said bushing rotatable therewith, and having an open side,illuminating means Within said reflector, a transparent chart arrangedover said open side, and indicating means for indicating the angularposition of said chart, said chart having a series of narrow darkparallel lines thereon spaced apart a distance substantially greaterthan their width, the spaces between said lines -being contrastedthereto by being lighter than said lines.

3. Arr astigmometer of the class described, comprising a rotatablehollow bushing carrying a reflector and a transparent illuminated chart,a source of light within said reflector for illuminating said chart androtatable therewith, a stationary cap over the end oi' said rotatablebushing, an operating member for rotating said bushing extendingtherethrough in alignment with the axis of said bushing and connected tothe inside thereof by a web which leaves a clear space of at leastadjacent said web and peripherally of said bushing, whereby a light cordmay extend through said cap to said source of light, past said web,without being engaged by said web during the rotation of said bushing.

THEODORE A. BENNETT.

